1. Field of the Invention
The present invention relates to an automatic power control circuit for a laser beam of an optical disk apparatus, and in particular, to an optical disk apparatus having an automatic power control circuit for a laser beam in accordance with ringing or waveform rounding, and a method of controlling the optical disk apparatus.
2. Description of the Related Art
In an optical disk apparatus, a method of controlling the intensity of a laser outgoing beam involves the detection of an outgoing laser beam, and control thereof by an APC circuit in which a front monitor signal proportional to a quantity of the detected laser beam is made to be an input. Because the outgoing beam varies at a high speed during the time of recording data, the outgoing beam is sampled-and-held by sampling pulses in the APC circuit, and the APC circuit is made to actuate at respective levels of the recording level/erasing level/reproducing (bottom) level. Further, in the case of rewritable type media such as CD-RWs, DVD-RWs, and the like, because a laser outgoing beam varies between multi-pulses at a high speed when multi-pulses are used, samplings are not sufficient for the situation. Therefore, control of an outgoing beam is stably carried out by using a bottom hold circuit.
However, the signal quality of a front monitor signal inputted to the APC circuit is easily affected in the above-described control method. In particular, there arises an error between a desired outgoing laser beam and a controlled outgoing laser beam due to a factor such as ringing, waveform rounding, or the like. In contrast thereto, a related technique corresponding to waveform rounding in a monitor signal has been known.
In the Patent Document (Jpn. Pat. Appln. KOKAI Publication No. 2002-109733) which is a prior art, there is disclosed a recording/reproducing apparatus for an optical disk apparatus which controls a read level at the time of a light mode. Here, a quantity of shift of a monitor signal is detected while carrying out recording, and a read level at the time of a light mode is optimized.
However, in the prior art of Patent Document 1, because detection of a quantity of shift of a monitor signal is carried out simultaneously with usual processing being carried out, processing in which a pulse width of a laser beam is adjusted in order to detect the quantity of shift, or the like is not carried out. Accordingly, there is the problem that detection of a quantity of shift of a monitor signal cannot be carried out in the optimum state. Further, in the prior art of Patent Document 1, detection of a quantity of shift of a monitor signal for optimizing a light level of a laser beam at the time of a light mode is not carried out, but detection of a quantity of shift for optimizing a read level is carried out. Accordingly, there is the problem that harmful effect of ringing or waveform rounding for a writing level at the time of light mode cannot be solved.